In conjunction with increases in transmission speeds and volumes in recent years, optical network systems that utilize an OTN (optical transport network: ITU-T G.709) to perform wavelength division multiplexing (WDM) have been put to practical use.
The OTN is a technology in which client signals based on SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy), Ethernet®, or the like are used and frames having a hierarchical structure are generated to perform data transmission suitable for WDM.
There are also demands for a protection scheme for achieving high-speed restoration of a communication during a failure. In known ring networks for transmission of SONET/SDH signals or the like that are not wavelength-multiplexed, protection schemes, such as BLSR (Bidirectional Line Switched Ring: Telcordia GR-1230-CORE) and MS SPRING (Multiplex Section Shared Protection Ring: ITU-T G.841, have been employed.
In those protection schemes, a path is looped back at nodes at two opposite ends of a failed link to avoid the failure. If such a protection scheme is simply applied to a WDM ring network, multiple protection rings configured for respective wavelengths operate interpedently. This results in an increase in the amount of processing load, thus making it difficult to realize high-speed restoration.
Thus, the ITU-T G.808.1 group protection scheme may be applied to an OTN WDM ring network. In this approach, when a failure occurs in signal light in a group of signal light in multiple wavelengths, paths for the signal light in all of the wavelengths in the group are switched at once to thereby realize high-speed restoration.
As related art, Japanese Laid-open Patent Publication No. 2001-156821 discloses a technology for a wavelength-multiplexed ring network. In this technology, control-information analysis at an intermediate node along a communication route is omitted to thereby simplify failure restoration processing. Japanese Laid-open Patent Publication No. 2002-77049 discloses a technology for switching, during redundant switching, routes for optical signals at a time for each unit of wavelength-multiplexed light.